Yes, this is more complicated than it initially sounds. For what it's worth, I'm not sure what system fonts are really necessary for Windows XP to function reliably either. Personally, I keep /System/Library/Fonts/ intact, even though Apple has said in the past that some of them aren't "necessary". If you have a Classic System Folder, then keep Charcoal, Chicago, Geneva, and Monaco in /System Folder/Fonts/.
I've also tested the suggestions within this document without trouble.
http://dl.extensis.com/downloads/SC/EN/P/Fonts_Best_Practices_in_OSX.pdf
In my experience, removing all Asian language support can create a situation where the 10.4 Finder may crash when it is asked to display Asian glyphs. The amusing thing is that the Asian font names themselves use these glyphs, so it can be a trick to put them back. I don't keep anything in /Library/Fonts/ or /Users/(your username)/Library/Fonts/. Although, sometimes people like to keep common MS fonts like Arial and Verdana active at all times because they are commonly specified in webpages. If they aren't available, webpages will fall back to another font.
There should probably be a wiki article on this...